Reactor Internal Pump is used for controlling Reactor core flux of a Nuclear reactor, in the boiling water reactor. The reactor internal pump is fitted by hanging down on lower part of a reactor pressure vessel. About ten sets of reactor internal pumps are arranged in circle form at the lower part of the reactor pressure vessel. The reactor internal pump is usually driven by an inverter.
The reactor internal pump consists of an impeller that is a hydraulic power part, and a motor (motor rotor and motor stator) that is a drive part. A reactor internal pump is contained in a cylindrical motor casing, and this casing is connected with a reactor pressure vessel through a nozzle, and hung down. The lower end of the motor casing is sealed by a motor cover, to thereby prevent the discharge of reactor water.
Conventionally, such a reactor internal pump has measured vibration, in order to supervise an operation state. Two kinds of vibration are measured by setting a vibration meter in the motor casing. That is, vibration of the motor casing produced by change of a pump axis and the fluid included therein is measured by an electrodynamic vibration meter (vibration detector), and the vibration sound and fluid sound of a pump is measured by piezoelectric vibration meter (sound detector). As for the vibration detector and the sound detector, two pieces are fitted on the circumferential direction of the motor casing at intervals of the angle of 90 degrees, respectively.
Object of the vibration detector is to measure vibration in the radial direction of the motor casing (reactor internal pump), and the object of the sound detector is to check the sound transmitted mainly to the motor casing.
By the way, an axial torsional vibration is generated in the reactor internal pump, due to the torque change of a motor. There is a possibility that the frequency component of the axial torsional vibration generates mechanical resonance with the natural frequency of the composition parts forming the reactor internal pump, and damage the composition parts. Therefore, taking into consideration the influence of repetitive fatigue of a reactor internal pump or the like, it is needed to measure the axial torsional vibration.
Measuring an axial torsional vibration of a motor by change of the phase difference of the detected signal of the optical detector, having the optical detector fitted on two places of the axis of rotation, is known, for example, as disclosed in JP-A-07-5056.
The conventional technology includes the optical detector fitted on the axis of rotation of a motor, to thereby measure the axial torsional vibration. However, both of the pump and the motor are contained in a motor casing, so as to be sealed therein. The reactor internal pump includes no exposed part in the axis of rotation. This makes it very difficult practically for a detector to be fitted. For enabling the detector to be fitted on the axis of rotation, large alteration of the reactor internal pump is needed.
For this reason, development of the technology for allowing an easy measuring system without large alteration of the reactor internal pump is demanded strongly.